We demonstrate an array operation of 20 nm self-selecting memory (SSM) for the first time. SSM shows extremely high cell performance, great reliability, and promising scalability below technodes of 1z nm. The innovation of material engineering enables memory-selector duality, which can reduce the aspect ratio (AR) and consequently lead to better scalability. Read window margin (RWM), the main hurdle for high density array operation, was successfully obtained by cell stack materials engineering with the help of bipolar write operations. Sufficient RWM can be obtained even below a write pulse of 20 ns for both Set and Reset, and at a much lower write current than the conventional 3D cross-point memory (3DXP), which guarantees extremely low write latency and power consumption. Owing to the low write current and short write pulse, SSM also displayed superior write cycle endurance, compared with conventional 3DXP. Due to the elimination of phase change material (PCM), SSM showed no write disturbance (thermal disturbance), and this can improve the total system power consumption and performance as well.